EP 322,049 A1 describes a nickel/silica catalyst which may, if desired, contain a cation of a metal X from group II of the Periodic Table of the Elements (IUPAC version). Mg is described as being the particularly preferred X. The catalyst is distinguished in its reduced state by an SiO.sub.2 :Ni molar ratio of (0.15 to 0.35):1, an X:Ni molar ratio of (0 to 0.15):1, an active nickel surface area of more than 120 m.sup.2 /g, a BET surface area wherein at least 40% of the pores have a pore radius above 2.5 nm (25 .ANG.) and a nickel content of at least 50%. In particular, the percentage of the surface having pores of a pore radius r.sub.P above 2.5 nm (25 .ANG.) is supposed to be important for the activity and selectivity of the catalyst. This percentage should be at least 40% and preferably exceed 45%.
The catalysts are prepared by adding, in a first step, a basic precipitant in excess continuously to a solution containing nickel salts and magnesium salts and then, in a second step adding aqueous silicate solution continuously to the coprecipitate thus obtained, collecting the precipitate formed, for example by filtration, and then drying and reducing it. The residence time to be observed in each case is short. It is 20 to 120 seconds in the first step and 40 to 300 seconds in the second step.